1. Field of Invention
The present invention is directed to oriented strand board (OSB) technology and, more particularly, to a structural panel with OSB faces and a core inside that is lightweight, strong, and a product of recycled (or other low cost) materials. The present invention also relates to a method of manufacturing such a composite board.
2. Description of the Related Art
The oriented strand board (OSB) has recently become a preferred product for structural wall sheathing. It is made by consolidating, under high pressure and temperature conditions, a thick mat of essentially flat wood flakes (otherwise called wafers) mixed with a small quantity (preferably between 2% and 6%) of a thermoset resin binder (usually of phenol formaldehyde or polyisocianate type). The mat is laid out in several layers on a continuous conveyor, so that each subsequent layer has a different preferred orientation of wood flakes. Larger flakes are usually reserved for faces on both sides, while smaller ones are placed in the middle layer (designated as the core).
The process of consolidating the OSB is made in one pressing step. This is in contrast to plywood (the more expensive predecessor of OSB) which is made by laminating together flat veneer sheets with a thermoset resin in between. It is believed that the required strength characteristics, such as modulus of elasticity (MOE) and the modulus of rupture (MOR), are mostly determined by the strength and integrity of the outmost layers in OSB panel, (i.e. the face). Although the core contributes to performance, its main purpose is to provide resistance to compression during the manufacturing press cycle. In particular, proper resistance to compression allows for effective face consolidation during the squeezing between the hot metal plate of the press and the densified core.
On the other hand, the dense core contributes to panel weight and consumes wood, a valuable resource. Replacing the conventional core with different materials, especially the products of recycling, has been and remains an attractive alternative for the industry and society as a whole.
Incorporating recycled plastics, paper waste and other comminuted materials into the core of a structural panel has been described in patent literature since 1972. For example, U.S. Pat. No. 3,650,871 (incorporated herein by reference) aims at producing a continuous mat by filling voids in the pre-fabricated honeycomb network with filler material for subsequent consolidation into a solid insulating board, to be further reinforced by pre-fabricated flexible covers on both sides, which are attached in a separate assembly step. However, the intentional filling of void space adds weight, and the manufacturing process for producing such a board requires more than one step.
Another example is described in U.S. Pat. No. 3,664,076 (incorporated herein by reference), which describes a product prototype that is a thick, but light structure, made from tom and randomly oriented waste paper pieces. It is made rigid by impregnating the paper pieces with resin, and subsequently bonding them to adjacent surface skins. However, to allow for sufficient rigidity and resistance to compression, significant amounts of resin are required. In addition, the only way an OSB face could be part of the proposed structure would be by conventional lamination of pre-fabricated faces and cores.
The manufacture of particle boards or variable shaped molded materials using paper waste is disclosed in U.S. Pat. No. 4,111,730 (describing an essentially homogeneous particleboard, made by using a conventional OSB production process, where thin wood wafers are replaced with pieces of recycled paper), and in U.S. Pat. No. 5,215,625 (utilizing complex recycling of paper, paint, and ink waste in the form of a moldable semi-liquid paste, which is subsequently placed in a mold and the residual solvent mixture is dried off). These two patents are incorporated herein by reference.
U.S. Pat. Nos. 3,671,615; 3,718,536; and 4,045,603 (all incorporated herein by reference) disclose technology for producing fiber reinforced thermoplastic boards. However, the produced structures are essentially homogeneous and usually very dense. In addition, both the manufacturing processes and the board properties are quite different from structural board manufacturing, which relies on thermoset resin technology and ordinarily delivers higher strength (especially at elevated temperature).
Still more examples of using recycled materials include U.S. Pat. No. 4,709,781 (describing multi-layer board made of metal sheets and comminuted scrap rubber tires), U.S. Pat. No. 5,011,741 (describing a multiple liner board bonded with starch), U.S. Pat. No. 5,209,968 (describing a plastic core between cellulosic covers, which is monolithically formed by using cementitious binder slurry, e.g., Portland cement, which is formed and cured), U.S. Pat. No. 5,611,882 (describing a water-based moldable composition made of cellulose fibres and soybean protein binder), and U.S. Pat. No. 5,729,936 (describing preparation of a prefabricated fibre-based core, to be combined in a next step by laminating with conventional wallboard). These five patents are incorporated herein by reference. These patents, however, do not disclose boards that offer an ideal combination of weight reduction, sufficient strength, and the ability to be produced in one manufacturing step.
U.S. Pat. No. 4,382,108 (incorporated herein by reference) describes production of a board with a core made from scrap plastic particles sandwiched between wood wafers and consolidated in one step by using polyisocianate resin binder. However, the core does not contain macro-voids, and is expected to be at least 50% heavier than an ordinary OSB panel of similar dimensions.
Accordingly, there is a need for an improved product and process that offers the combination of weight reduction, sufficient strength, and the ability to make the product in one pressing step which is preferable because it helps minimize production costs.